Logic gates: basic functions for all logic design. Truth tables and logic circuits: defining what circuits do, building circuits from definitions. Karnaugh maps: a cleverer way to build circuits. Important logic blocks: high- level parts than just gates. Example: building a memory array: putting together the important logic blocks. Example: building a counter: using state and clocks. A logic gate is an elementary building block of a digital circuit. Most logic gates have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels. Xor out when a b = 1. Xor out when a b = 0. Note: truth tables define the behavior of the gate (it" s output) for all possible input combinations. We got the complete truth table by brute force trying all the inputs.